A field experiment on winter barley (Hordeum vulgare L., cv Ponente) under three water regimes (full irrigation, 50% and rainfed) and two nitrogen levels (0 and 120 kg/ha) has been carried out in Valenzano (Bari), in order to investigate resources use efficiencies in terms of water, nitrogen and radiation. During the whole season, N supply affected growth, development and yield much more than water applications. It was due to high precipitation regime (395 mm) with important rainfall events occurred at the most sensible phenological stages. Consequently, water stress occurred only between milk and dough maturity stages, without significant effects on yield production. Both radiation and water use efficiencies have been improved by N supply. Results from a simplified N balance indicated that the amount of N supplied to barley exceeded the effective N fertilization requirement for optimizing marketable yield.
